JP4332440B2 - Light emitting diode manufacturing method, light emitting diode - Google Patents

Description

  The present invention relates to a method for manufacturing a light emitting diode and a light emitting diode.

  In order to increase the light quantity of the light emitting diode, it is important to improve the light extraction efficiency from the light extraction surface of the light emitting diode.

As a method of improving the light extraction efficiency, by forming irregularities on the light extraction surface, the critical angle at the light extraction surface when extracting light from the light emitting diode to the outside is relaxed, and reflection at the light extraction surface is reduced. There are ways to reduce it. As a method for forming the unevenness, a method by irradiating an energy beam such as a laser (for example, refer to Patent Document 1), a method by fine pattern formation by block copolymer and etching by RIE (for example, Patent Document 2) See).
No. 2003-218394 No. 2003-218383

  However, in the method using irradiation with an energy beam such as a laser, there is a concern that the light emitting diode may be damaged by the energy beam.

In addition, in the method of forming a fine pattern using a block copolymer and etching using RIE, there is a concern about the complexity and stability of the manufacturing process. Is provided in a simple and stable manner.

  The light emitting diode manufacturing method of the present invention includes (1) laminating a light emitting layer, a current diffusion layer, and a cap layer in this order on a substrate, (2) forming a plurality of stripe-shaped V grooves in the cap layer, 3) A step of forming a plurality of stripe-shaped V grooves in the current diffusion layer by chemically etching the current diffusion layer starting from the groove bottom of the V groove of the cap layer is provided.

  According to the present invention, first, a plurality of stripe-shaped V grooves are formed in the cap layer, which is an upper layer of the current diffusion layer, and the current diffusion layer is chemically etched starting from the groove bottom of the V groove of the cap layer. The starting point of chemical etching of the current spreading layer can be made very elongated. Since the starting point is very elongated, a plurality of V-grooves having good stripes can be formed in the current diffusion layer.

  The light emitting diode manufacturing method of the present invention includes (1) laminating a light emitting layer, a current diffusion layer, and a cap layer in this order on a substrate, (2) forming a plurality of stripe-shaped V grooves in the cap layer, 3) A step of forming a plurality of stripe-shaped V grooves in the current diffusion layer by chemically etching the current diffusion layer starting from the groove bottom of the V groove of the cap layer is provided.

  First, the step (1), that is, the step of forming the light emitting layer, the current diffusion layer, and the cap layer on the substrate in this order will be described.

  The substrate is made of a compound semiconductor substrate such as GaAs or an elemental semiconductor substrate such as Si. The conductivity type of the substrate may be N-type or P-type. The light emitting layer, current spreading layer, and cap layer are preferably formed on the (100) plane of the substrate. In this case, it is easy to form V-grooves in the current diffusion layer and the cap layer in a later step.

  The light emitting layer formed on the substrate can be formed, for example, by forming a first cladding layer, an active layer, and a second cladding layer in this order. The light emitting layer preferably has a double heterojunction structure, but may have a single heterojunction structure or a homojunction structure.

  Each layer forming the light emitting layer, the current diffusion layer, or the cap layer is made of a compound semiconductor such as a binary compound semiconductor such as GaAs or GaP, a ternary compound semiconductor such as GaAlAs or AlInP, or a quaternary compound semiconductor such as AlGaInP. Become. Each layer forming the light emitting layer is preferably epitaxially grown by MOCVD, MBE, or the like. The “current diffusion layer” is a protective layer formed mainly for the purpose of protecting the light emitting layer, or an antireflection formed mainly for the purpose of reducing the reflection of light from the light emitting layer on the light extraction surface. A layer having a function other than current spreading, such as a layer, is also included. The cap layer is preferably formed of a material or composition different from that of the current spreading layer.

  Here, the thickness of the current diffusion layer is preferably 3 μm or more. If it is smaller than 3 μm, the current spread becomes worse and the external light extraction efficiency is lowered. Further, the thickness of the cap layer is preferably 1 to 5 μm. If it is out of this range, there is a concern that the etching control in the next process becomes difficult.

  In addition, another layer such as a buffer layer, an insulating layer, a protective layer, or a current blocking layer may be formed between two adjacent layers of the substrate, the light emitting layer, the current diffusion layer, and the cap layer.

  Further, the phrase “on the substrate” includes a concept of contacting the substrate, contacting the semiconductor substrate through a protective film, an insulating film, or the like, or contacting the semiconductor substrate and not contacting the semiconductor substrate. The same applies to other phrases such as “on the membrane” and “on the layer”.

  Moreover, it is preferable to provide the process of forming an electrode on the obtained board | substrate after a process (1). The electrode is a P-type or N-type electrode. The electrode may be formed via a contact layer. The P-type electrode can be formed by a method including a step of vapor-depositing AuZn or the like to form an alloy. The N-type electrode can be formed by a method including a step of vapor-depositing AuGe or the like and forming an alloy.

  Next, the step (2), that is, the step of forming a plurality of stripe-shaped V grooves in the cap layer will be described.

  The plurality of stripe-shaped V grooves refers to, for example, a plurality of V-shaped elongated grooves extending substantially in one direction. The plurality of stripe-shaped V grooves are preferably formed substantially parallel to the <011> direction of the substrate. This is because it is easy to form a V-groove whose slope is the (111) plane of the cap layer. Further, it is preferable that the plurality of stripe-shaped V grooves are substantially equally spaced. The width of the plurality of stripe-shaped V grooves is preferably 1 μm or more. If it is smaller than 1 μm, the patterning accuracy is lowered and the variation becomes large. The pitch at which the plurality of stripe-shaped V grooves are formed is preferably 3 to 15 μm. This is a geometric result according to the cap layer thickness.

  The size of each V groove may be different. The “V-groove” includes not only a case where the tip is sharp but also a case where the tip is rounded. The groove bottom of the V groove may or may not reach the current diffusion layer. If not reached, the etching of the V-groove is advanced in a later step, and after the current diffusion layer is exposed to the cap layer side, the etching of the current diffusion layer is started. A state in which the V-shaped pointed tip has just reached the current diffusion layer is suitable.

  For example, the plurality of stripe-shaped V-grooves include a step of forming a resin layer having a stripe-shaped opening in the cap layer by photolithography and etching techniques, and chemically etching the cap layer through the stripe-shaped opening. Can be formed. In order to form a plurality of stripe-shaped V grooves in the cap layer substantially parallel to the <011> direction of the substrate, the stripe-shaped openings may be formed substantially parallel to the <011> direction of the substrate. preferable. The striped openings are preferably formed at substantially equal intervals. The width and pitch of the stripe-shaped openings are preferably about 1.3 to 1.5 × L (μm) when the cap layer thickness is L (μm). In this case, it is possible to form the maximum number of stripe shapes.

  The chemical etching of the cap layer is performed using, for example, a mixed solution of ammonium hydroxide, hydrogen peroxide, and water. The chemical etching of the cap layer is preferably performed using an etching solution that increases the etching selectivity of the cap layer to the current spreading layer. This is because if the current diffusion layer is largely etched in the step of forming a plurality of stripe-shaped V grooves in the cap layer, it is difficult to form good V grooves in the current diffusion layer.

  Next, the step (3), that is, a step of forming a plurality of striped V grooves in the current diffusion layer by chemically etching the current diffusion layer starting from the groove bottom of the V groove of the cap layer will be described. To do.

  As described above, the groove bottom of the V groove of the cap layer may or may not reach the current diffusion layer. When the groove bottom of the V groove of the cap layer reaches the current diffusion layer, that is, when the current diffusion layer is exposed to the cap layer side, chemical etching of the current diffusion layer starts from the exposed portion. Is done.

  When the groove bottom of the V groove of the cap layer does not reach the current diffusion layer, the current diffusion layer is not exposed to the cap layer side at first. Therefore, first, etching of the V groove of the cap layer is advanced to expose the current diffusion layer to the cap layer side, and then etching of the current diffusion layer is started. In this case, when chemical etching is performed using an etchant that reacts with both the current diffusion layer and the cap layer, the V groove of the cap layer is first etched, and the current diffusion layer is exposed to the cap layer side as it is. After that, the etching of the current spreading layer can be started.

  The chemical etching is performed using an etching solution that reacts with both the current diffusion layer and the cap layer, and preferably using an etching solution with substantially the same etching rate for the current diffusion layer and the cap layer. preferable. This is because the cap layer can be removed at the same time as forming the V-groove in the current diffusion layer. This chemical etching can be performed using a mixed solution of phosphoric acid and hydrogen peroxide.

  The current spreading layer is chemically etched starting from the groove bottom of the V groove of the cap layer. Therefore, the starting point of chemical etching of the current diffusion layer can be made very long. Since the starting point is very elongated, a plurality of V-grooves having good stripes can be formed in the current diffusion layer. The V-groove of the current diffusion layer is, for example, one using a forward mesa portion of the crystal structure.

  Further, when the plurality of stripe-shaped V grooves of the cap layer are formed substantially parallel to the <011> direction of the substrate, the plurality of stripe-shaped V grooves of the current diffusion layer are also formed in the <011> direction of the substrate. Are formed substantially parallel to each other. In this case, the V groove of the current diffusion layer includes a slope having an inclination according to the (111) plane of the current diffusion layer. Further, in this case, the plurality of stripe-shaped V grooves of the current diffusion layer have slopes including a plane that is 50 to 65 degrees with respect to the normal line of the light extraction surface. The “V-groove” includes not only the case where the bottom of the V-groove of the current diffusion layer is sharp but also the case where the current groove is round. The “V-groove” includes a case where the edge of the V-groove is rounded. In the manufacturing method of the present invention, since the crystal plane of the current diffusion layer is used, the V-groove can be formed stably and uniformly. In addition, since the manufacturing method of the present invention uses chemical etching, it is suitable for mass production.

  Moreover, it is preferable that the plurality of stripe-shaped V grooves in the current spreading layer are substantially equally spaced. The width and pitch of the plurality of stripe-shaped V grooves are preferably about 1.3 to 1.5 × L (μm) when the cap layer thickness is L (μm). In this case, it is possible to form the maximum number of stripe shapes.

  Through the steps so far, a light emitting diode in which a plurality of stripe-shaped V grooves are formed on the light extraction surface of the current diffusion layer can be manufactured. In this light emitting diode, since a plurality of stripe-shaped V grooves are formed on the light extraction surface, the critical angle at the light extraction surface when light is extracted from the light emitting diode to the outside is relaxed, and the light extraction surface The reflection of is reduced.

  In this light emitting diode, the light extraction efficiency by the antireflection film is not improved, but the critical angle at the crystal interface is relaxed by adding a V-groove. Even in this case, the reflectance can be reduced.

  Moreover, it is preferable to further include a step of forming irregularities on the slope by treating the slope of the V groove of the current diffusion layer with an acid solution after the step (4).

The treatment with the acid solution can be performed using a hydrochloric acid solution or the like. By this treatment, irregularities are formed on the slope of the V groove of the current spreading layer. This unevenness is usually finer than the pitch at which a plurality of stripe-shaped V grooves in the current diffusion layer are formed.
Through the steps so far, a light emitting diode in which irregularities are formed on the slope of the V-groove can be manufactured. In this light emitting diode, since the irregularities are formed on the slope of the V-groove, the reflection on the light extraction surface is further reduced.

  Moreover, the process of grinding the back surface of a board | substrate may be further provided, and the process of forming an electrode in the back surface of the obtained board | substrate may be provided. The electrode is a P-type or N-type electrode. The electrode may be formed via a contact layer.

  The description so far is mainly for the case where a plurality of stripe-shaped V grooves are formed in the current diffusion layer. However, not only when a plurality of stripe-shaped V grooves are formed in the current diffusion layer, but also when a plurality of stripe-shaped V grooves are formed on the light extraction surface of the light-emitting diode, in general, light emission The light extraction efficiency from the light extraction surface of the diode can be improved. That is, a protective film, an antireflection film, or an insulating film may be formed on the current diffusion layer or instead of the current diffusion layer, and a plurality of stripe-shaped V grooves may be formed on the light extraction surface of the film. Good.

  Therefore, according to the present invention, a light emitting diode having at least a light emitting layer and having a plurality of stripe-shaped V grooves formed on the light extraction surface of the light emitting diode is provided. Moreover, such a light emitting diode can be basically manufactured by the method described above. The description so far applies in principle also to such a light emitting diode and its manufacturing method.

  FIG. 1 is a cross-sectional view showing a manufacturing process of a light-emitting diode according to Example 1 of the present invention.

First, the following layers are formed on a substrate 1 made of an N-type GaAs substrate (100).
Buffer layer 3 : N-type GaAs (carrier concentration: 5 × 10 ¹⁷ cm ⁻³ , layer thickness: 0.5 μm)
Light-emitting layer 5 : N-type Al _0.5 In _0.5 P cladding layer 5a (carrier concentration: 5 × 10 ¹⁷ cm ⁻³ , layer thickness: 1.0 μm), undoped (Al _0.3 Ga _0.7 ) _0.5 In _0.5 P active layer 5b (layer) (Thickness: 0.6 μm) and P-type Al _0.5 In _0.5 P clad layer 5c (carrier concentration: 3 × 10 ¹⁷ cm ⁻³ , layer thickness: 1.0 μm)
Current diffusion layer 7 : P-type GaP (carrier concentration: 50 × 10 ¹⁷ cm ⁻³ , layer thickness: 10.0 μm)
Cap layer 9 : P-type GaAs (carrier concentration: 10 × 10 ¹⁷ cm ⁻³ , layer thickness: 3.0 μm)

  Next, the P-type electrode 11 is formed on the epi-wafer surface with the P-type ohmic material AuZn and the bonding pad material Au. In the process of forming the electrode 11, material deposition, photolithography, electrode material etching, and alloying were performed as usual. The electrode arrangement is 280 μm × 280 μm.

  Next, a resist 12 having a stripe pattern with a width of 3 μm and a pitch of 6 μm parallel to the <011> direction of the substrate is formed by photolithography on the surface of the epitaxial wafer on which the P-type electrode 11 is formed, and FIG. Get the structure shown.

Next, the cap layer 9 on the epi-wafer surface is chemically etched with a 30 ° C. mixed solution of NH ₄ OH: H ₂ O ₂ : H ₂ O = 1: 1: 10. Thereby, the V-groove 13 is formed in the cap layer 9, and the structure shown in FIG. 1B is obtained.

Next, the epitaxial wafer surface is chemically etched using a 60 ° C. mixed solution of H ₃ PO ₄ : H ₂ O ₂ = 3: 1. At this time, the current diffusion layer 7 and the cap layer 9 are etched. As shown in FIG. 1C, the etching of the current diffusion layer 7 starts from the tip 15 of the V groove 13 of the cap layer 9 formed earlier, and the etching proceeds while showing a normal mesa shape. To do. Further, the side etching of the cap layer 9 proceeds simultaneously, and the cap layer 9 other than the vicinity of the electrode 11 is finally removed. At this stage, the current diffusion layer 7 is exposed on the epi-wafer surface. In addition, a plurality of stripe-shaped V grooves 17 are formed on the epi-wafer surface in a direction substantially parallel to the <011> direction of the substrate, and the structure shown in FIG.

  In the method of this embodiment, since the plurality of stripe-shaped V grooves 17 are formed using the crystal structure, the plurality of stripe-shaped V grooves 17 can be formed uniformly in the wafer surface. Here, since the P-type electrode 11 uses an Au-based material and does not act on the two kinds of etching solutions, it is not necessary to protect the P-type electrode 11 by photolithography. When using an Al electrode, it is necessary to protect the Al electrode from the above etching solution with a photoresist or the like. In this case, the process is not complicated by using a photomask in which stripes and electrode patterns are combined.

  Next, when the surface of the epitaxial wafer on which a plurality of stripe-shaped V grooves 17 are formed is further treated with a 70 ° C. HCl solution, the slope 19 of the V grooves 17 has an unevenness of about 0.5 μm on average (not shown). ) Is formed. At this time, when the electrode 11 is formed of an Au-based material, the electrode 11 is not eroded by the 70 ° C. HCl solution.

  Next, the wafer is lapped to a desired thickness, and AuGe is deposited and alloyed as an N-type GaAs side electrode. Next, the wafer is diced in accordance with the arrangement pitch of the P-type electrodes 11 to complete the chip fabrication.

  The light emitting diode was manufactured using the above method. The size of the light-emitting diode manufactured this time is 280 μm × 280 μm × 240 μmt, and the diameter of the bonding pad is 100 μmφ. In the conventional structure, it was about 50 mcd / 590 nm, but in the structure manufactured this time, 75 mcd / 590 nm was obtained. In addition, φ5 lamps were produced using these chips, and their luminosities were compared. As a result, 500 mcd was obtained with respect to the conventional 400 mcd.

  In the present embodiment, the AlGaInP-based LED structure on the GaAs substrate is used. However, the AlGaInP-based LED structure on the GaP substrate and the AlGaInP-based LED with the metal bonding structure can also obtain the effect on the light extraction efficiency. Further, LEDs other than AlGaInP-based LEDs are also possible.

FIG. 2 is a cross-sectional view illustrating a manufacturing process of the light-emitting diode according to the second embodiment.
The difference between the second embodiment and the first embodiment is that the cap layer 9 is formed thick in the second embodiment.

  First, using the same material as in Example 1, the semiconductor layers 3, 5, 7, and 9 are stacked, and then the P-type electrode 11 is formed. Next, a resist 12 having a stripe pattern with a width of 3 μm and a pitch of 6 μm parallel to the <011> direction of the substrate is formed by photolithography on the surface of the epitaxial wafer on which the P-type electrode 11 is formed, and FIG. Get the structure shown.

Next, the cap layer 9 on the epi-wafer surface is chemically etched with a 30 ° C. mixed solution of NH ₄ OH: H ₂ O ₂ : H ₂ O = 1: 1: 10. As a result, the V-groove 13 is formed in the cap layer 9 to obtain the structure shown in FIG. At this time, the tip 15 of the V groove 13 of the cap layer 9 does not reach the current spreading layer 7.

Next, the epitaxial wafer surface is chemically etched using a 60 ° C. mixed solution of H ₃ PO ₄ : H ₂ O ₂ = 3: 1. At this time, first, the etching of the cap layer 9 proceeds in the direction indicated by the dotted arrow. When the etching of the cap layer 9 proceeds and the current diffusion layer 7 is exposed, the etching of the current diffusion layer 7 starts.
The subsequent steps are the same as in the first embodiment.

It is sectional drawing which shows the manufacturing process of the light emitting diode which concerns on Example 1 of this invention. It is sectional drawing which shows the manufacturing process of the light emitting diode which concerns on Example 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 3 Buffer layer 5 Light emitting layer 7 Current diffusion layer 9 Cap layer 11 Electrode 12 Resist 13 V groove 15 Groove bottom 17 V groove 19 Slope

Claims (6)

(1) A light emitting layer, a current diffusion layer, and a cap layer are stacked in this order on a substrate, and (2) a plurality of stripe-shaped V grooves are formed in the cap layer by chemical etching using a first etching solution. 3) A plurality of stripe-shaped V-grooves are formed in the current diffusion layer by chemically etching the current diffusion layer starting from the groove bottom of the V-groove of the cap layer with a second etching liquid different from the first etching liquid. The manufacturing method of a light emitting diode provided with the process to do. The manufacturing method according to claim 1, wherein step (2) is a step of forming a plurality of stripe-shaped V grooves in the cap layer substantially parallel to the <011> direction of the substrate. The manufacturing method of Claim 1 which further comprises the process of forming an unevenness | corrugation on an inclined surface by processing the inclined surface of the V-groove of an electric current diffusion layer with an acid solution after a process (3).   The manufacturing method according to claim 1, wherein the first etching solution is an etching solution that increases an etching selectivity of the cap layer to the current diffusion layer.   The manufacturing method according to claim 1, wherein the second etching solution is an etching solution that reacts with both the current diffusion layer and the cap layer.   The manufacturing method according to claim 5, wherein the second etching solution is an etching solution having substantially the same etching rate with respect to the current spreading layer and the cap layer.

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